The present invention relates to a scroll fluid machine and particularly to a scroll fluid machine in which a fixed wrap of a fixed scroll in a housing engages with an orbiting wrap of an orbiting scroll rotatably mounted around an eccentric axial portion of a driving shaft, the orbiting scroll being eccentrically revolved with the driving shaft so that a gas sucked from the circumference or center of the housing is compressed or expanded towards the center or circumference.
JP2004-308436A discloses a scroll fluid machine having an orbiting scroll comprising an orbiting end plate having an orbiting wrap on each surface, and JP7-42953B2 discloses a scroll fluid machine in which an orbiting wrap projects on only one surface of an orbiting end plate.
In the former, during operation, a tip seal on the top of the fixed wrap of the fixed scroll slidably contacts each surface of the orbiting end plate under almost the same condition, so that almost the same pressure is applied to cause almost the same heat. Thus, each surface of the orbiting end plate is unlikely to stretch locally or be curved to prevent unsmoothing in operation or decrease in efficiency, or the tip seal of the fixed scroll is unlikely to wear unequally to prevent performance from decreasing or prevent vibration or noise.
However, as described in JP7-42953B2, in the orbiting scroll having the orbiting wrap only on one surface, a bearing boss projects on the rear surface of the orbiting end plate, so that the orbiting end plate is unequally deformed or stretched or causes angles of the orbiting wrap to differ locally owing to pressure load, friction with the tip seal of the fixed scroll or unequality on generated heat.
Thus, the orbiting wrap contacts the fixed end plate with deviation to cause variation in pressure locally reducing efficiency or involving noise, heat or vibration. Furthermore, the tip seals of the fixed and orbiting scrolls locally wears to decrease duration.
To prevent the orbiting end plate from deformation during operation, it is necessary to increase thickness of the orbiting end plate significantly. However, in the orbiting scroll, the orbiting end plate is manufactured integrally with the orbiting wrap by die casting from Al metal. With large thickness of the orbiting end plate, during cooling after die casting, cooling speed of the orbiting end plate and orbiting wrap becomes nonuniform, so that the angle of the orbiting wrap becomes different locally to decrease efficiency thereby speeding up wear or causing noise.
Furthermore, in the center of the rear surface of the orbiting end plate, an eccentric axial portion of the driving shaft is mounted via a ball bearing and a known pin-crank-type self-rotation preventing device is mounted at three positions equally spaced on the rear surface of the orbiting end plate. It is necessary to provide a supply hole for grease for each of the bearings horizontally, and it is troublesome for the grease to put in the bearing via the holes.